The present invention relates to a radio transmission device which has function for performing directional transmission and to a transmission directivity adjusting method.
Generally, a propagation path of a digital radio communication system consists of many multi-paths. For that reason, the propagation path in the digital radio communication system has a frequency characteristic for a transmission line. Concretely, the propagation path in the digital radio communication system has a transmission characteristic of selectivity to the frequency. Furthermore, when a communication terminal device moves like a mobile station, these characteristics change in accordance with a lapse of time with motion of the communication terminal device. As a result, the reception signal undergoes effect of different fading within the bandwidth. The fading is called as a selective fading.
It is necessary to take countermeasure to the selective fading. There is the adaptive-array technique for the countermeasure of the selective fading. The adaptive-array technique is a technique that it allows a plurality of antenna elements to be prepared, and the plurality of antenna elements receive the signal, subsequently, it causes the reception signal to be weighted before combining.
Furthermore, there is the transmission directivity control technique. In such the transmission directivity control technique, the signal is transmitted while employing the same radiation pattern as the reception radiation pattern on the basis of the weight factor of the reception signal, which is combined while utilizing the above-described adaptive-array technique. In this transmission directivity control technique, since it allows the signal not to be transmitted in the direction of arrival of the unnecessary signal, the transmission side is capable of securing the multi-path propagation path. For that reason, it comes unnecessary to provide advanced technique that it allows the equalizer and so forth to be equipped at the receiver (terminal side). Furthermore, it allows the signal not to be transmitted in the direction of arrival of the unnecessary signal, therefore, the area which the transmitted radio wave reaches is limited, thus it enables the frequency utilization efficiency of the downlink to be improved.
There is described the radio transmission device having the transmission directivity control function while employing FIG. 1. As shown in FIG. 1, in the radio transmission device, the modulation circuit 1 modulates the transmission signal, before sending the modulation signal to the vector multipliers 3 to 5 for performing the directional transmission. Here, the vector multiplication is the processing that it permits the amplitude and the phase of the transmission signal to be changed for the directional transmission. When the transmission is the directional transmission in which it allows only the phase to be altered, such the directional transmission is called as the phase shift type transmission to be exact. However, in this case, the vector multiplication is universally employed. Consequently, also it causes the phase shift type transmission to be described as the vector multiplication.
The vector multipliers 6 to 8 multiply the respective modulation signals obtained from the vector multipliers 3 to 5 on the basis of the weights from the transmission weight circuit 2 and the correcting weight circuit 21 by the transmission weight for the directional transmission, thus sending the signal after multiplication toward the transmission RF circuits 9 to 11.
The transmission RF circuits 9 to 11 input therein the signal after multiplication. In the transmission RF circuits 9 to 11, it causes the frequency conversion for the transmission carrier frequency and the amplification to be executed with respect to the inputted signal. The frequency conversion is performed in such a way that it permits the frequency to be adjusted while employing the frequency source 12. The transmission signal is transmitted from the antennas 16 to 18 passing through the distributors 13 to 15.
In order to perform the directional transmission accurately, the vector difference among the respective antennas in the output of the vector multipliers 6 to 8 and the vector difference among the respective antennas in the antenna output terminals are required to be the same vector difference. When the vector differences are different, it is incapable of executing the directional transmission in the right direction. However, in some cases, the outputs of the vector multipliers 6 to 8 pass through the respective transmission RF circuits 9 to 11, therefore, the vector difference among the respective antennas in the antenna output terminals differ from the vector difference among the respective antennas in the outputs of the vector multipliers 6 to 8.
Formerly, there is the method for adjusting the directional transmission while correcting such the vector differences. As shown in FIG. 1, it permits the signal to be extracted from the distributors 13 to 15 immediately in front of the antennas 16 to 18, before causing the signal to be converted into the same frequency as that of the output of the vector multipliers 6 to 8 at the reception RF circuit 19 while employing the same frequency source as that of the transmitter. Further, the phase and the amplitude immediately before transmission of the converted signal are measured in the measuring device 20 to compare with the phase and the amplitude to be the output of the vector multipliers 6 to 8. This processing is performed in every respective antennas. According to the operation, it is capable of obtaining errors which appear caused by passing through the transmission RF circuits 9 to 11.
Furthermore, it permits the correction value to be determined for correcting the amplitude and the phase of the respective antennas while taking the phase and the amplitude about one of any antennas to be the reference. Then, the correcting weight circuit 21 stores therein the correction value. The correction values are sent to the vector multipliers 3 to 5. The correction values are employed as it permits the transmission weight sent from the transmission weight circuit 2 to be corrected. Moreover, in order to detect differences of the amplitude and the phase among the respective antennas, respective phases and amplitudes in respective measuring sections of the measuring device 20 are necessary to be adjusted in the same value.
However, in such the adjusting method, on the occasion of the measuring, connection of the connector or so forth becomes necessary, therefore, adjustment becomes complicated, further there is the problem that it is necessary to adjust the phase and the amplitude in every connection of the connectors.
On the other hand, in order to cause the change of connection of the connector to be unnecessary, it is preferable to prepare the reception RF circuit as many as the number corresponding to the number of the antennas (in the example, three antennas), however, generally, it is very difficult to prepare a plurality of the reception RF circuits whose amplitude characteristic and phase characteristic are entirely the same.
In view of the foregoing, it is an object of the present invention, in order to overcome the above-mentioned problem to provide a radio transmission device and transmission directivity adjusting method in which change for connection of the connectors on the occasion of adjusting of the phase and the amplitude can be dispensed with, and it is capable of correcting characteristic of the amplitude and the phase by only one reception RF section.
The subject matter of the present invention is that it causes the transmission directivity to be adjusted while employing correction values of the antenna. The correction values of the antennas are obtained as follows. The distributor immediately in front of the antenna distributes the signals of the respective antennas. It permits the signals to be combined for generating combined signal. Subsequently, it causes the correction value of the respective antennas to be obtained while employing the combined signal and the reference signal. It allows the correction value of the respective antennas to be obtained such that difference between the phase of the combined signal and the phase of the reference signal become the minimum value and that difference between the amplitude of the combined signal and the amplitude of the reference signal become the minimum value. The correction value of the antenna is updated employing newly obtained correction values. Thus, the transmission directivity is adjusted while employing these correction values.